PQuest Post Clean Recovery and Sapphire Carriers

Jim McVittie mcvittie at snf.stanford.edu
Wed Mar 29 12:46:04 PST 2006


To help develop a post wet clean recovery process for the PQ, I have attached a
recommended procedure for the Lam etcher. I have also included an in-situ plasma
clean procure for the Lam.
I actually have 2 more in-situ plasma clean procedures for the Lam but I only have
hard copies of them.

Presently, most of the III-V users are using bare Si wafers for their carriers.
This means that they are adding some SiCl4 to their etch process. The good thing
about doing this is that SiCl4 is a useful additive to GaAs etching. On the down
side, Si is a III-V dopant and the exposed Si carrier is changing the free Cl
concentration around the sample. At other universities, sapphire carrier wafers are
sometimes used to avoid the effects of etching the carrier. I have some 4" sapphire
wafers if someone wants to try changing carriers. The change will most likely
affect the etch results plus you will change the apparent bias voltage.


Jim McVittie wrote:

> Ed,
> I think improved maintenance of the PQ is fine but one has to be careful of not
> get into unintended consequences, which degrade etch processes. One really does
> not want to be opening a Cl etch chamber unless one has to. There are 2 issues.
> First, you will introduce water from the cleaning process and second, you will
> change the surface chemistry of the chamber walls. Some processes are very
> sensitive to the water level in the chamber and all the processes are sensitive
> to wall surface chemistry. So the result is it takes a good effort to get a
> chamber back to where it should be after a wet clean.  For the Lam etcher, we
> were given a 2 page procedure from Lam called “Post We-Clean Chamber Recovery
> and Seasoning” to be done after every wet clean. This procedure recommends
> running 25 wafers under various conditions.  Although we are not going to run
> 25 wafers through this system, we need to develop a similar procedure for the
> PQ.  I recommend that any chamber cleaning be based on process needs and not on
> an arbitrary time bases.
>     Jim
> Ed Myers wrote:
> > PQuest Users,
> >
> > Does the PQuest community want the SNF staff to schedule regular preventive
> > maintenance on the PQuest chamber?
> >
> > A month ago Ceser cleaned the PQuest chamber after we received some
> > complaints on repeatability of an etch process.  Apparently, this had a
> > very positive effect on the user's etch.  The SNF staff would like to take
> > on more responsibility in maintaining the chamber condition, if it is
> > agreeable with the PQuest community.  I'm told that manual cleaning of the
> > chamber is very unpleasant.  The proposed approach would mix in manual
> > chamber cleans along with evaluation of a shutdown-chamber clean recipe
> > similar to what Elmer added to the AMT etcher.
> >
> > We will plan on implementing a preventive maintenance program unless we
> > hear objections from the PQuest user community.  We are also looking for a
> > champion to help us design and evaluate the effects of any preventive
> > maintenance.
> >
> > Regards,
> > Ed
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